Environmental Engineering Reference
In-Depth Information
Plate 22.3
A 'swidden' or burnt patch made by shifting
cultivators in tropical rain forest in Sarawak. Crops will
benefit from the nutrients in the ash 'fertilizer'.
Photo: Ken Atkinson.
Nutrient cycles within the rain forest are radically altered by human clearance for
agriculture. The traditional peasant system is that of shifting cultivation, whereby a patch
of forest is burned on a rotation basis (Plate 22.3). Crops are cultivated for several years
in the burned area, until it is abandoned, allowing the forest to reinvade. The patch may
be reused on a twenty- to thirty-year rotation. The essence of this 'slash and burn' system
is that the nutrients in the biomass are quickly released into the soil and litter
compartments of the cycle. Harvesting of the crops then takes nutrients, as well as
energy, out of the system. Even if fertilizers are added, the effects are temporary, and
cropping of the patch becomes unsustainable after a
